1. Field of the Invention
The present invention relates to an oxygen permeability measuring apparatus and method, and defect inspection apparatus and method. More particularly, the present invention relates to an oxygen permeability measuring apparatus and method, and defect inspection apparatus and method, which is capable of measuring or inspecting oxygen permeability even for a very small oxygen amount.
2. Description Related to the Prior Art
Quality of food and/or drugs will drop when oxidation occurs. It is well-known to use an oxygen barrier material for packaging the food with a small value of an oxygen permeation rate, for example, 10−2 cc/m2·day·atm. Thus, the food is packaged by use of an oxygen barrier film formed from the oxygen barrier material, or a container formed from the oxygen barrier material as an oxygen barrier container.
Examples of known methods of measuring the oxygen permeation rate of the oxygen barrier material are a differential pressure method and equal pressure method (JIS K 7126). According to those, a chamber is split into two areas by use of the oxygen barrier material as a sample material of the measurement. In the first area, oxygen is introduced. In the second area, oxygen permeated through the sample material is monitored by use of a pressure sensor. Furthermore, JP-A 54-130091 discloses a method in which the sample material is formed in a bag shape. Inert gas is filled in the sample material which is left to stand in the atmosphere. Let the first area be an outer area of the atmosphere. Let the second area be the inside of the bag. When a predetermined time elapses, an oxygen amount in the second area is measured by an analyzer, so as to measure the oxygen permeation rate of the sample material.
Also, JP-A 54-111390 and JP-A 2007-010382 disclose a detection method of detecting presence of a defect in the oxygen barrier material, or a portion where oxygen is easy to permeate. In the detection, the container is filled with a substance of developing color upon occurrence of the oxidation or reduction. The container is exposed to the atmosphere having oxygen, for example the atmospheric air. The defect of the container can be discovered according to a position of a colored portion of the substance.
New attempts are made today for producing an optical device and electronic device by use of a substrate of an organic film in contrast with the well-known use of an inorganic substrate. This will make it possible to lower the cost of the substrate, reduce the thickness, and raise the flexibility. Recent needs for enlargement of products and wearable products may be satisfied when the organic film is used.
Various requirements occur with a new use of the organic film for a substrate of the electronic device. A problem lies in an oxygen barrier property of the organic film. If the organic film has only a low value of the oxygen barrier property, the electronic device may be broken by oxygen transmitted through the organic film. Accordingly, the oxygen barrier film is required between the organic film and the electronic device. Furthermore, the electronic device must be covered with the oxygen barrier film. The oxygen permeation rate of the SiNx film used presently for protecting the electronic device is approximately 10−2 cc/m2·day·atm. However, in view of environmental compatibility of the electronic device, it will be necessary for a protection film to have the oxygen barrier property at a level of the oxygen permeation rate of 10−4 cc/m2·day·atm for a solar cell, and 10−6 cc/m2·day·atm for an inorganic EL element. Those types of the oxygen barrier material will have such a high performance that a conventional technique of evaluation cannot evaluate. No method of precise evaluation of the performance of the oxygen barrier material has been known.
The oxygen permeation rate of a very low level is required also for an organic EL element for use in an organic EL display panel, oxygen barrier film for a solar cell, oxygen barrier film for electronic paper, and the like.
A serious problem lies in the method of JP-A 54-130091 for evaluating the performance of the oxygen barrier material. Very longtime will be required for acquiring sufficient oxygen density for the measurement, because of a rate determining value of the detecting performance of the pressure sensor. According to the disclosed information, the measurement is conducted for 30 days in a range of 0.8-44.7 cc/m2·day·atm. JP-A 54-111390 and JP-A 2007-010382 disclose a method of estimating the oxygen permeation rate by use of leuco methylene blue as a color developer for coloring upon the oxidation. In the method, the container of a normal shape is prepared. A needle with a diameter of 0.2 mm is thrust in the container at a depth of 0.05 mm so that a hole is formed as a portion of a reduced thickness. The portion of the hole has a smaller oxygen barrier property than the remaining portion with a normal thickness. A component of the leuco methylene blue disposed behind the hole develops blue color, which indicates a drop of the oxygen barrier property. However, there arises a problem in the method in that the oxygen barrier property at the hole cannot be quantified for evaluation even after detection of the hole. Also, an apparatus for delivery of gas is required and will excessively enlarge the entire size of the system according to the method determined in the JIS (Japanese Industrial Standards).